不同养护制度下活性粉末混凝土早期收缩的模型研究

发布时间：2018-03-10 05:16

本文选题：活性粉末混凝土　切入点：早期收缩　出处：《北京交通大学》2017年硕士论文　论文类型：学位论文

【摘要】：活性粉末混凝土由于采用较低的水胶比、剔除粗骨料、掺加大量的超细活性掺合料及高掺量复合外加剂等原因,早期收缩远大于普通混凝土材料,存在较高的早期开裂风险。为探究活性粉末混凝土的收缩发展规律并明确其收缩机理,准确的对活性粉末混凝土的收缩进行预测和计算,本文针对分别对常温(25℃)浸泡、密封、干燥三种条件下材料的早期收缩进行了测量,并结合内部相对湿度、水化程度、孔结构分布和力学性能,对收缩机理进行分析并建立收缩预测模型。在此基础上研究了不同养护温度(25℃、40℃、75℃)对浸泡、密封、干燥三种养护条件下活性粉末混凝土材料早期收缩的影响,探讨了不同养护条件下的收缩发展规律与变化机理。论文主要工作和结论如下:(1)测量了常温条件下活性粉末混凝土在干燥、密封、浸泡条件下的收缩,结合内部相对湿度、水化程度和孔结构变化对其机理进行分析。结果表明:活性粉末混凝土的早期收缩受养护条件的影响较大,不同养护条件下,收缩的发展均呈前期增长较快,后期逐渐变缓趋势,但收缩发展速率、时间及收缩值的大小均不相同。(2)密封条件与干燥条件下的收缩发展规律呈现出较大的差异,密封条件下,28d内收缩持续发展,而干燥条件下,前6d收缩发展较快,6d到28d内发展缓慢;从水化角度分析,密封条件下在28d内水化反应是持续进行的,自收缩也持续发展,而干燥条件下由于水分散失导致7d后水化反应发展缓慢,自收缩的发展也受到限制;从数值上看,到28d时密封条件下的收缩值比干燥条件还要高出90.5με,与普通混凝土中规律恰好相反;结合水化进程、孔结构及内部水分迁移等微观试验结果,进一步探讨了早期收缩规律的微观机理。(3)基于胶凝材料水化程度、内部相对湿度、弹性模量、孔隙结构分布等参数,分别建立了化学收缩、自收缩及干燥收缩预测模型。以实测浸泡组的收缩应变为基准,标定了密封与干燥条件下的化学收缩值;以实测密封组的收缩应变为基准,标定了干燥条件下的自收缩值,实现了三种收缩的分离。(4)测量了三种不同的养护温度(25℃、40℃、75℃)下,长期置于干燥、密封、浸泡三种条件中活性粉末混凝土的收缩,结合水化程度分析了养护温度对活性粉末混凝土化学收缩、自收缩、干燥收缩的影响。不同养护温度对化学收缩、自收缩和干燥收缩的影响均不相同;随着温度的升高,化学收缩逐渐增大,但增长的幅度不大;在浸泡条件下,较高的温度会引起较高的早期自收缩;高温对自收缩存在抑制作用,且温度越高,抑制作用越明显;在前期,干燥收缩随着养护温度的升高而增加,但高温导致结构更加致密,抑制了后期收缩的发展。(5)结合养护温度对三种收缩的影响,对高温蒸养条件下的收缩规律进行分析。随着养护温度的升高,早期收缩也会随之提高,且在湿度较高的环境中养护后,养护结束时短期内会造成较大的收缩,温度越高,该阶段的收缩值越大,成为造成开裂风险的主要原因;后期的材料收缩发展规律显示,养护温度越高,后期的体积稳定性越好,收缩值的变化值越小。
[Abstract]:Reactive powder concrete due to the low water cement ratio, excluding coarse aggregate, because adding a large number of Co doped superfine active material and high content of composite admixture, early shrinkage is far greater than ordinary concrete materials, there is a higher risk of early cracking. In order to explore the development regularity of shrinkage of reactive powder concrete and clear its shrinkage the mechanism of shrinkage of reactive powder concrete accurate prediction and calculation, this paper respectively at room temperature (25 DEG C) soaking, sealing, early shrinkage drying under the three conditions of the material are measured, and combined with the internal relative humidity, water level, pore distribution and mechanical properties, analyze the mechanism of shrinkage and the establishment of shrinkage prediction model. On the basis of different curing temperature (25 DEG, 40 DEG, 75 DEG C) to soak, sealing material, influence of shrinkage of reactive powder concrete early drying three kinds of curing conditions, exploration To discuss the development and change rule of the shrinkage mechanism under different curing conditions. The main work and conclusions are as follows: (1) measuring the ambient temperature conditions of reactive powder concrete in drying, sealing, soaking condition contraction, combined with the internal relative humidity, degree of hydration and pore structure of the mechanism was analyzed. The results show that effect of reactive powder concrete early shrinkage by curing conditions greatly under different curing conditions, the development of shrinkage was increased faster in early and later gradually slowed the trend, but the shrinkage rate, time and shrinkage of big and small are not the same. (2) the contraction law of the development of sealing conditions and drying conditions under the present a large difference between the sealing conditions, contraction of sustainable development in 28d, and the drying conditions, before the contraction of 6D development, 6D to 28d in the slow development of hydration; from the angle of analysis, under the conditions of sealing in 28d in response to Continued the self shrinkage of sustainable development, and dry conditions caused by 7d after hydration reaction of the slow development of the loss of water, since the contraction of the development is limited; from the point of view, to 28d under the conditions of sealing shrinkage than drying conditions also higher than 90.5 Mu epsilon, contrary to common concrete rules in combination; hydration process, pore structure and internal moisture migration microscopic test results, to further explore the mechanism of early shrinkage rules. (3) based on the degree of hydration of cementitious material, internal relative humidity, elastic modulus, distribution of pore structure parameters, chemical shrinkage prediction model are established respectively, the autogenous shrinkage and drying in order to shrink. The shrinkage strain measured immersion group for the benchmark calibration of chemical shrinkage and dry sealing conditions; shrinkage strain measured with the seal group as a benchmark, calibration of the autogenous shrinkage and drying conditions, three kinds of realization Contraction of the separation. (4) three different curing temperature was measured (25 C, 40 C, 75 C), long-term in a dry, sealed, reactive powder concrete for three conditions of contraction, with the degree of hydration of curing temperature on reactive powder concrete chemical shrinkage, autogenous shrinkage, drying effect shrinkage. Different curing temperature on chemical shrinkage, self shrinkage and dry shrinkage are not the same; with the increase of temperature, the chemical shrinkage increases gradually, but little growth; in the soaking condition, the autogenous shrinkage of early high temperature causes higher temperature; on the autogenous shrinkage has inhibitory effect, and temperature the higher, the more obvious inhibition effect; in the early stage of drying shrinkage increased with increasing curing temperature, but high temperature leads to more compact structure, suppressed the late shrinkage. (5) combined with the effect of curing temperature on three kinds of shrinkage, high temperature steam curing. Under the rule of shrinkage were analyzed. With the increase of curing temperature, shrinkage will increase, and maintenance in high humidity environment, resulting in a greater contraction of the short term maintenance at the end, the higher the temperature, the phase of the contract value is bigger, become the main cause of the cracking risk; display material the law of the development of shrinkage, curing temperature is higher, the better volume stability of the late change shrinkage value is smaller.

【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

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